U.S. Pat. No. 4,027,669 describes a thermoplastic syringe barrel with an integral thermoplastic sleeve that is internally threaded for aiding and holding a needle or the like to a tapered adapter of the barrel. Circumferentially spaced slots in the sleeve permit the sleeve to flex outwardly during its moulding process for longitudinally stripping the sleeve from its mold without requiring expensive unscrewing machinery. This strip ejection process for the nonslotted sleeve is described in British Pat. No. 1,086,763 (U.S. Pat. No. 3,402,713).
Separately formed locking sleeves, which were subsequently bonded to the syringe barrel and were not laterally flexible for strip mold ejection, sometimes included external grooves for registering with the expensive unscrewing mechanism on the molding machine, as shown in U.S. Pat. No. 3,542,024. It is also an expensive process to subsequently bond the locking sleeve to the syringe barrel.
The integral thermoplastic retention sleeves must be sufficiently flexible for longitudinally stripping from the molding die without substantially distorting the internal threads. The sleeve must also have sufficient resistance against outward flexibility to prevent flanges or ears of a needle from stripping out of the sleeve's threads. To insure this latter feature, the sleeve of U.S. Pat. No. 4,024,669 had to be made with a thick wall section; i.e., approximately 0.050 inch. Such wall thickness in the sleeve was at the borderline of flexing sufficiently for mold removal, but still stiff enough for hypodermic needle retention. Because of this thick wall section, the molding cycles had to be relatively long for the plastic to cool in the collar prior to ejection, thus increasing manufacturing costs.